This invention relates to the structure of a reflective liquid crystal display, and in particular to the structure of such a display that has only one polarizer.
A conventional liquid crystal display is shown in FIG. 1. Such a conventional display normally comprises both a front polarizer 1 and a rear polarizer 4. A liquid crystal cell is placed between these polarizers 1,4 and the cell in turn comprises two sheets of transparent glass 2,3 held apart by spacers 7 and containing the liquid crystal 6. A voltage applied to the liquid crystal cell controls the polarization of the light and this voltage is applied through two transparent conductive coatings 14,15 formed on the insides of the two glass sheets 2,3 facing the liquid crystal 6. A diffusive reflector 16 is placed behind the rear polarizer 4 for viewing the display from the front.
In U.S. Pat. No. 5,926,545 Kwok et al disclose a new type of reflective liquid crystal display where there is only one front polarizer 1 and the rear polarizer can be omitted. This design is shown in FIG. 2. In this arrangement it is necessary for the reflector 8 to be placed inside the liquid crystal cell and the reflector 8 must meet a number of requirements.
In particular, it is necessary for the reflector to reflect incident light with good efficiency. It has to be conductive and patternable into various electrode shapes and configurations for the application of a voltage to the liquid crystal cell. The patterned electrodes and the background also have to be of the same colour and shade for the design to be aesthetically pleasing. Additionally the rear reflector may be textured to give a degree of scattering of light.
According to the present invention there is provided a reflective liquid crystal display comprising a liquid crystal cell formed of a liquid crystal material disposed between first and second substrates, wherein said first substrate is optically transparent and is formed with a coating of optically transparent and electrically conductive material on the side of said first substrate facing said liquid crystal material, said coating being further provided with a liquid crystal alignment layer, and wherein said second substrate is formed with a plurality of coatings on the side of the second substrate facing the liquid crystal material, said coatings comprising in sequence a layer of metallic reflective material deposited on the surface of the second substrate, a layer of an electrically insulating material, a layer of an optically transparent and electrically conductive material, and a liquid crystal alignment layer.
The electrically insulating layer is preferably made to be thick enough (about 1 micron) to avoid the possibility of any pinholes that form a short between the metallic reflective layer and the electrically conductive layer. As a further protection, however, the metallic reflective layer may be divided into electrically isolated regions (for example a regular geometric pattern of squares, rectangles, circles or polygons).
Possible materials for the reflective material include aluminium, gold, silver, chromium, tin, zinc and iron.
The metallic reflective layer may be formed by sputtering in a partial vacuum or by vacuum evaporation. The deposition conditions may be controlled to give a partially light scattering surface. The metallic layer may have a thickness of between 0.01 and 1 micron.
Possible materials for the electrically insulating layer include silicon oxide, aluminium oxide, magnesium oxide, zirconium oxide or titanium oxide. The insulating layer may also be formed of an organic polymer material.
Possible materials for the electrically conductive layer include conductive oxides such as indium tin oxide, tin oxide, zinc oxide, gallium oxide or indium gallium oxide. The conductive layer could also be formed of the same material as the metallic reflective layer.
According to another aspect the present invention provides a reflective liquid crystal display comprising a liquid crystal cell formed of a liquid crystal material disposed between first and second substrates, wherein said first substrate is optically transparent and is formed with a coating of optically transparent and electrically conductive material on the side of said first substrate facing said liquid crystal material, said coating being further provided with a liquid crystal alignment layer, and wherein said second substrate is formed with a plurality of coatings on the side of the second substrate facing the liquid crystal material, said coatings comprising in sequence a layer of electrically insulating reflective material deposited on the surface of the second substrate, a layer of an optically transparent and electrically conductive material, and a liquid crystal alignment layer.
The electrically insulating reflective surface may be provided with a partially light scattering surface and may be formed of a dye-doped polymer material.
According to a further aspect of the present invention there is provided a reflective liquid crystal display comprising a liquid crystal cell formed of a liquid crystal material disposed between first and second substrates, wherein said first substrate is optically transparent and is formed with a coating of optically transparent and electrically conductive material patterned into strips on the side of said first substrate facing said liquid crystal material, said coating being further provided with a liquid crystal alignment layer, and wherein said second substrate is formed with a plurality of coatings on the side of the second substrate facing the liquid crystal material, said coatings comprising in sequence a layer of metallic reflective material deposited on the surface of the second substrate and patterned into parallel strips, and a liquid crystal alignment layer.